Process of treating latex impregnated paper with an isocyanate and resultant article



PROCESS OF TREATiNd LATEX IMPREGNATED PAPER WITH AN ISOCYANATE AND RESULTANT'ARTICLE Filed May 11, 1954 July 28, 1959 N 4 HAYES Em 2, 97,094

A l O 1 U I IMPREGNATED PAPER LATEX MENTOR NORMAN J.HAYE$ WILLIAM c. oss

ATTORNEY PROCESS OF TREATING LATEX HVIPREGNATED PAPER WHTH AN ISOYANATE AND RESULT- ANT ARTIQLE Norman J. Hayes, Arlington, and William C. Ross, Winchester, Mass., assignors to W. R. Grace & Co., a corporation of Connecticut Application May 11 1954, Serial No. 429,119

6 Claims. (Cl. 117-62) This invention relates to improvements in latex-treated paper.

Latex-treated papers are used in considerable quantity, largely in substitution for leather. Typical uses include insoles, midsoles, welting, heel pads, and plumper material in the shoe industry and as a base for the manufacture of artificial leather.

Such papers are normally manufactured from a pulp having a high alpha cellulose content (usually 80% or more), which has been but lightly beaten upon dispersion of the pulp fiber in water in a paper beater. Beating to a freeness of 7 to 15 seconds Williams is typical if the paper is to be saturated when dry. Sulfite and sulfate pulps are also used particularly if the latex deposition takes place in the paper beater, in which case, the beating may be continued until a higher freeness is achieved. Most of these papers are wet-laid felts made on normal paper-making machinery, but considerable quantities of air-laid felts are also used as saturating base and usually are converted into hathands and stays. For this reason, the term paper, as used herein, includes cellulosic felts of both wet or dry origin, for our process is equally useful with webs of either type.

There are three ordinary methods of impregnating paper with latex to form latex-treated papers. The latex may be added to the paper-making slurry in the beater, in which case the rubber is coagulated on the surface of the fibers, for example, by the addition of alum. The paper is formed from the treated slurry.

Latex-treated paper may also be formed by the Wet web process, in which the web is passed through an impregnating bath inserted in a paper-making machine after the web is formed, and the excess water has been removed but before the paper has been dried. Finally, latex-treated paper may be formed by the dry web process, in which a finished, dry impregnating paper is resaturated with a latex composition and then redried. Dry web impregnation is the characteristic manner of latex-treating air-laid felts. Latex-treated papers made by any of these three processes appear to be equally suitable for use in practicing the present invention.

All these materials are extremely strong when dry, often exceeding the strength of and giving superior performance to leather; but unless they are coated with pyroxlin or the like, they are inferior to leather in abrasion resistance and are greatly weakened when they become wet.

We have discovered that it is possible to make these useful materials equally strong whether they be wet or dry and to increase their resistance to wet abrasion at least l,000%. We accomplish these results by further impregnating, or at least wetting, latex-treated papers with a solution of an isocyanate. As will appear from the data which follows, this treatment not only improves the wet strength and wet abrasion resistance characteristics of the product of a startling degree but also improves the strength, flexibility, and durability thereof. Indeed, in some cases, the strength of the treated web even after States Patent I prolonged immersion in water heated to 160 F. is equal to its dry strength within the limits of accuracy of tensile testing techniques. Equally significant, none of these benefits are gained at the expense or loss of any preexisting properties of the latex-treated paper.

The effectiveness of the treatment depends upon two factors: the quantity of rubber impregnant and the quantity 'of isocyanate in the treating solution. The treatment appears to be efiective with the various types of paper coming within the scope of the term latex-treated paper, irrespective of whether a conventional wet strength agent is utilized or not. It is likewise eifective "with the various types of latex useful for impregnating paper; with paper impregnated according to any of the conventional methods; with all available isocyanate resins and With any of the solvents useful for forming solutions of such isocyanates.

To assure uniformity of results, each of the tests enumerated herein was made according to the following procedure. Eight inch by ten inch sheets of a paperimpregnation base which contained no wet strength agent were impregnated by total immersion with a latex impregnating compound. This compound in each case, unless otherwise designated, was of 30% total solids and contained a latex of the designated rubber and minor amounts of stabilizer, anti oxid-ant, dormant coagulant, dye and a levelling agent for the dye-all according to conventional latex compounding practice. In each case, the total rubber hydrocarbon solids exceeded about of the total solids in the impregnating compound. The impregnated sheet was drained, placed between sheets of blotting paper, and passed through a roller to simulate the squeeze roll used in commercial practice. The paper was then dried to bone dryness at a temperature of approximately 230 F. The dried latex-impregnated paper, after being maintained for at least overnight at normal temperature and humidity, was heated to a temperature of 300350 F. in a circulating air oven for 2 to 3 minutes immediately before treatment to eliminate any possible variation that may be caused by differences in moisture content. It should be noted that this latter step is taken merely as a precaution, since samples of dried, impregnated paper, which have been conditioned in air at normal temperatures but at relative humidity, and even samples subjected to live steam have been treated with isocyanate resin solution with no significant variation in result from those obtained with the bone dry paper.

The dried sheets were then treated with a solution of an isocyanate resin. On a laboratory scale this was done by immersion, by spraying, or by roll application of the solution. Each method is equally effective, but of course, the effectiveness of the treatment depends upon the completeness of the saturation of the paper. After treating, the wet sheet was placed between two sheets of blotting paper as before and passed under a roller to remove the excess fluid. The sheets were again dried in contact with a surface heated to a temperature of about 230 F. and conditioned in air at normal temperature and humidity overnight.

Heating is not essential but merely provides an easy method of removing the solvent. Samples dried at various temperatures ranging between room temperature and 350 F. have shown no noticeable difierence in properties provided there had been substantially complete solvent removal. .f

The tensile strength and elongation of the samples were then measured both wet and dry on a Scott tensile tester model X-3. The wet samples were soaked in water at a temperature of F. for the time indicated. The measurements were made on strips V2" by .4 with a one-inch initial gap between the jaws and with a rate of elongation of 12 inches per minute. The tensile is reported in pounds corrected to an equivalent 1" strip, and the elongation is reported as elongation at break in percentage elongation. All tests were run in the machine direction of the paper.

To show the effect caused by various types of isocyanates, impregnating paper was impregnated with a 30% total solids impregnating compound containing GR-S latex type 2001 according to the procedure out lined above. The sheets were then treated With a 2 /2% solution in toluene of each of six difierent typical isocyanates. These were the following:

Phenyl isocyanate (PI) Octa-decyl iso cyanate (ODI) OH3(OH2)11NC O Alpha-naphthyl isocyanate (ANI) Methylene bis (4 phenyl isocyanate) (MDI) m-Tolylene diisocyanate (TDI) NCO NCO

Triphenyl methane triisocyanate (TPM) NCO An untreated sheet and one treated with toluene were used as controls. The tensile properties were measured both for the dry sheets and for sheets which had been soaked in water maintained at 160 F. for twenty-four This table clearly shows that, while treatment with any of the isocyanates results in improved strength without loss in extensibility of the treated paper, the effect is more noticeable in the case of the poly-isocyanates than in the case of the mono-isocyanates. Indeed, it will be noticed that the impregnated paper after treatment with a polyisocyanate solution is as strong, it not stronger, after a twenty-four hour immersion in Water at 160 F. than the impregnated but untreated paper when dry.

A word of explanation of the term percent isocyanate in sheet, appearing in Table I above and in several of the following tables, would appear to be in order. During the course of these tests, we have been unable to detect any significant change between the weight of a dry, untreated sheet and the weight of the same sheet after treatment. However, it has been noted that the concentration of isocyanate in the isocyanate solution remains unchanged as the solution is used up. Therefore, the quantity of isocyanate deposited upon the web has been estimated by weighing the sheet immediately before and immediately after treatment to obtain the total amount of solution imbibed by the web. The quantity reported as percent isocyanate in sheet is the weight of isocyanate in that amount of solution expressed as a percentage of the Weight of the dry, untreated sheet.

To show the effect of varying the quantity of isocyanate in the treating solution, the same impregnated paper as used above was treated with solutions of m-tolylene diisocyanate (TDI) in toluene of varying concentrations ranging from 0.00% total solids (straight toluene) to 100% total solids (straight TDI). Again the tensile characteristics were determined both for the dry sheet and for sheets soaked in water at 160 F. for twenty-four hours. An untreated sheet was again used for a control. The results of this test are tabulated in Table II.

TABLE II D Wet Percent ry Percentisocyanate isocyanate (TDI) 1n solution in sheet Tensile, Elonga- Tensile, Elongapounds tion, pounds tion,

percent; percent Untreated 70 25 12 33 0.00- 22 21 41 0.005 67 22 27 37 0.05 67 21 39 40 0. 24 70 20 55 43 0. 47 74 21 56 34 1. 2 81 21 76 40 2. 7 80 22 83 43 5. 2 77 27 83 45 9. 9 79 21 82 42 18.8 74 27 80 32 25. 9 22 75 31 25.9 78 22 73 26 12.9 77 20 32 It will be noticed that treatment with a solution of isocyanate as dilute as 5 of 1% results in a noticeable increase in the tensile strength of the treated impregnated paper when soaked in water at F. for twenty-four hours and that the maximum improvement in this property occurs when the treatment is carried out with solutions containing 5% or more of the isocyanate, there being very little change as the concentration further increases. Indeed, if anything, the etfectiveness decreases slightly as the percent of isocyanate in the sheet exceeds about 10%. The quantity of isocyanate deposited in the sheet failed to increase at concentrations above approximately 60% because of the difiiculty in obtaining complete saturation of the web at these concentrations. This, of course, indicates that complete saturation of the sheet is not necessary but is only desirable to obtain uniformity.

To show the effect of the isocyanate treatment upon papers impregnated with the various types of rubber ordinarily used for that purpose, samples were made up in which the impregnating paper was impregnated with 30% total solids impregnating compounds made fi'om the following rubber latexes:

Butadiene-styrene (GR-S latex type 2001) Butadiene-acrylonitrile (Hycar OR 25 1562) Neoprene (Neoprene N571) Natural (concentrated, centrifuged Liberian Hevea latex- Loxite 2109) v In addition to obtaining tensile values of the sample both dry and after soaking in 160 F. water for twentyfour hours, the tensile values were determined for samples which had been soaked in 160 F. water for seven days to show the effect of prolonged soaking. Parallel tests were run for each of the latex-impregnated sheets consisting of one sample without further treatment, one treated with toluene alone, and one each treated with a 1%, 2 /2%, and 5% solution, respectively, of m-tolylene diisocyanate in toluene. The results of this test are tabulated in Table III.

For convenience, the amount of latex impregnant deposited upon the paper has been reported throughout in terms of the concentration of the impregnating compound. In the case of the impregnant, impregnation with a 30% total solids GR-S compound results in an average increase in the Weight of the dry, impregnated sheet of approximately 71% based on the weight of the dry, unimpregnated sheet. The range for individual samples was between 68 and 74%. For butadiene-acrylonitrile the average is 70% and the range 66 to 74%. For neoprene the average is 85% with a range 85-86%, and for natural rubber the average is 71% and the range 70-72%.

TABLE III Tensile Percent Latex Treatment isocy- Dry Wet Wet anate in 1 day 7 days Sheet T. E. T. E. T. E.

Lb. Pct. Lb. Pct. Lb. Pct. Untreated- 62 28 7 48 6 45 Butadiene-sty- Toluene.-. 62 31 13 41 12 37 rene 1 TDI 0. 42 65 26 41 39 39 34 2% TDI 1.2 75 31 67 41 66 42 TDI- 2. 5 80 30 76 40 72 44 Untreated 62 30 11 32 32 Butadiene-aery- Toluene 62 35 17 45 42 lonitrile 1% TDI- 0. 65 77 42 61 55 64 60 2%% TDI 1. 6 76 40 67 62 66 68 5% TD 3. 3 79 45 78 53 79 41 Untreated- 80 19 9 28 7 29 Toluene 81 16 20 15 21 Neoprene 1% TDL 0. 58 99 27 34 27 2%% TDI 1. 4 100 21 32 27 TDI- 2. 9 97 20 44 25 47 31 Untreated 63 14 10 28 11 30 Toluene 79 20 31 36 31 32 Natural 1% 'IDL 0.46 80 18 48 32 49 39 2%% TDL- 1. 1 79 23 55 39 54 40 5% TDI- 2. 4 82 21 56 38 56 38 It will be noted that the improvement in the tensile strength of the water-soaked material characteristic of the isocyanate treatment of latex-impregnated paper occurs for each of the several rubbers used for impregnating the sheet.

There are two remaining variables: the effect due to varying the amount of the latex impregnant in the impregnated sheet and the efiect of different solvents for the isocyanate.

To show the effect of varying the amount of latex impregnant, sheets were impregnated with both GR-S and neoprene impregnating compounds having a total solids varying between 0 and 30%. Except for this change, the sheets were handled as outlined above. The various sheets were then treated with a 2.5% solution of m-tolylene diisocyanate (TDI) in toluene; and the tensile characteristics of the treated sheets, both dry and after soaking in 160 F. Water for twentyafour hours, were determined and compared in each case with those characteristics of the identical untreated sheets. The results of this test are tabulated in Table IV.

TABLE IV GR-S impregnated Untreated Treated with 236% TDI Percent solution Impregcomnant, pound total solids Dry Wet Dry Wet solids in sheet T. E. T. E. T. E. T. E.

Lb. Pct. Lb. Pct Lb. Pct. 0.00 52 11 0 10 7 10 0.02 38 9 0 12 19 15 0.11 40 12 1 14 32 20 0.21 49 16 2 18 42 23 0.41 53 23 4 23 53 29 0. 65 57 31 5 32 61 40 Neoprene impregnated Untreated Treated with 2%% TDI Percent solution Impregcomnant, pound tal solids Dry Wet Dry Wet solids in sheet '1. E. T. E. T. E. T. E.

Lb. Pct Lb. Pct Lb. Pct. Lb. Pct. 0.00 52 11 0 46 10 7 10 0. 03 43 11 3 10 46 11 14 12 0. 11 52 13 6 11 64 14 25 20 0. 22 62 13 6 10 79 18 31 23 0.45 71 20 8 20 84 22 36 23 0. 70 73 19 11 21 92 25 41 25 As this table shows, the eifectiveness of the treatment increases as the quantity of rubber solids contained in the latex-treated paper increases.

The effect of the use of a solvent for the isocyanate other than toluene to form a solution of the isocyanate is shown in Table V. In each case, a sheet impregnated with a 30% T.S. GR-S latex impregnant was used and was treated both with straight solvent and with a 2 /2% solution of m-tolylene diisocyanate in that solvent. As before, an untreated sample of the same paper was run as a control, and the tensile characteristics in each case were determined when the sample was dry and after the sample had been soaked in water at 160 F. for twentyfour hours.

TABLE V Untreated 2%% TDI Percent isocya- Solvent Dry Wet Dry Wet nate in sheet T. E. T. E. T. E. T. E.

. Lb. Pct Lb. Pct Lb. Pct

7 35 10 54 30 46 1.15 11 40 75 28 68 50 1.27 13 52 30 72 48 1.19 12 42 80 24 67 42 1.19 14 43 77 30 69 45 1. 27 VM 8: P naphtha 14 34 78 27 72 48 1. 15 Propylene dichloride 65 23 13 39 74 30 64 34 1.69 Carbon tetraehloride 72 23 14 33 75 26 73 40 2. 35

1 A high boiling petroleum hydrocarbon supplied by the Esso Standard Oil Company.

Apparently, the choice of solvent for the isocyanate is not significant in respect to the effectiveness of the re sulti-n g treatment.

To show the efiect of treatment upon abrasion resistance of sheets, samples were tested on a Gardner straightline washability and abrasion machine. In this machine a one-pound brush, measuring 3 inches by 1 /2 inches with Chinese hog bristles and weighing one pound, is drawn according to the procedure outlined above showed no appreciable Wear except a slight polishing after 13,000 complete cycles. However, when run in the presence of an amount of plain water just sufiicient to keep moist that area of the sheet in the region of the stroke of the brush, the untreated sheet started to show appreciable wear after 20 cycles; and the sheet, which was approximately 0.038 of an inch thick was completely worn through at the end of 594 cycles. Under identical conditions, the treated sheet showed no sign of wear at the .end of 1,000 complete cycles and only slight wear at the end of approximately 6,000 complete cycles when the test was discontinued. At this point the thickness of the "abraded portion of the treated sheet was reduced by 0.004 of an inch or approximately 10% In summary then, it has been shown that the properties of latex-impregnated cellulosic webs or, to use the common terminology, latex-treated paper, especially as re gards the abrasion resistance and tensile strength of that paper-when wet, are vastly improved if that paper is treated and preferably saturated with a solution of an isocyanate. This efiect appears to be independent of the exact type of rubber latex used to form the latextreated paper and to be independent of the exact type of organic isocyanate (e.g., an organic compound containing the terminal group NCO) used for treating the paper, although as might be expected the diand tri-isocyanates are more effective when compared on a weight basis than the monoisocyanates. The improvement in properties of the isocyanate-treated, latex-treated paper is progressive at a given latex impregnation, as the quantity of isocyanate deposited therein is increased with slight but noticeable improvements noted with treatment with solutions of an isocyanate in solvent as dilute as 0.01% and reading a maximum at a concentration between 2.5 and 5%. Likewise, the improvement in properties with treatment with a given solution of an isocyanate with paper impregnated With varying quantities of latex is progressive with increasing degrees of impregnation.

The drawing is a flow sheet illustrating the manner in which the preformed latex-impregnated paper is treated.

We claim:

1. The process for improving the characteristics of latex-impregnated paper wherein the latex is coagulated which comprises treating the said impregnated paper with a solution of an isocyanate, the latex impregnant of said paper being selected from the group consisting of natural and artificial rubber latex.

2. The process claimed in claim 1, wherein the iso cyanate is a polyisocyanate selected from the class consisting of the diand tri-isocyanates.

3. The process claimed in claim 2, wherein the poly isocyanate is m-tolylene diisocyanate.

4. The process claimed in claim 2, wherein thepolyisocyanate is triphenyl methane triisocyanate.

5. The process claimed in claim 2 wherein the polyiso cyanate is methylene bis (4 phenyl isocyanate).

6. As an article of manufacture, an isocyanate treated latex-impregnated paper having an improved resistance to wet abrasion prepared by the process of claim 1.

References Cited in the file of this patent UNITED STATES PATENTS.

2,107,304 Novak Feb. 8, 1938 2,282,827 Rothrock May 12, 1942 2,430,479 Pratt Nov. 11, 1947 2,439,514 Herndon Apr. 13, 1948 OTHER REFERENCES Lockwood: Supplemental Report on Applications of Diisocyanate, Fiat Final Report No. 1301, Sept. 15, 1947, pp. 5 and 6. 

1. THE PROCESS FOR IMPROVING THE CHARACTERISTICS OF LATEX-IMPREGNATED PAPER WHEREIN THELATEX IS COAGULATED WHICH COMPRISES TREATING THE SAID IMPREGNATED PAPER WITH A SOLUTION OF AN ISOCYANATE, THE LATEX IMPREGNATED OF SAID PAPER BEING SELECTED FROM THE GROUP CONSISTING OF NATURAL AND ARTIFICIAL RUBBER LATEX. 